1. Field of the Invention
The present invention relates to a control method and an apparatus wherein when controlling a driving of a sensorless and brushless DC motor, a present angular position of a rotor is correctly detected to heighten the reliability controlling a motor rotation, and an optimal driving current is provided to phase coils of the motor at an optimal point in time to improve the driving characteristics of the motor.
2. Description of the Prior Art
Generally, a sensorless and brushless motor is applied as a head drum assembly which is utilized for recording the video signals onto the tape and for reproducing the recorded video signals or as a capstan motor which is utilized for traveling the magnetic tape at a constant velocity.
FIG. 1 is block diagram for showing a configuration of a conventional circuit section for controlling a position of a sensorless and brushless DC motor. As shown in FIG. 1, the position control circuit section includes a switching section 30 which supplies Y-winding three phases of motor coils (hereinafter, referred to as "Y-winding three phase coils") 20, 21 and 22 with a test current for detecting the variation of inductances, i.e., a rotational position of a magnet rotor, of three phase coils 20, 21 and 22 included in motor 10, and with a driving current for rotating the magnet rotor.
In order to drive a switching-driving section 30, a controller 40 provides a pilot signal which is a train of square-waves having a short period to switching-driving-section 30.
When the test current is provided to a phase coil of three phase coils 20, 21 and 22 to which the driving current from switching-driving section 30 is not provided, i.e., in relation to the rotation of the magnet rotor, and which is inactive, a peak detector 50 detects a peak value of the test current which varies in accordance with the inductance variation of the phase coil. Then, since the inductance variation is very small, the variation of the test current is also very small. Therefore, before peak detector 50 detects the peak value of the test current, the varied test current is amplified by an amplifier 60.
The peak values of first and second test currents which are detected by peak detector 50 for each of the phase coils at first and second predetermined points in time are held for a time by a sample & hold section 70 independent of the variation of the first and second peak values.
The first and second peak values which are held by sample & hold section 70 are compared to each other by a comparator 80 and only a largest peak value is selected. The peak values which are selected by comparator 80 are stored in designated memory locations of first, second and third memories 90, 91 and 92.
Hereafter, a controller 40 reads and fetches the peak values which are recorded in first, second and third memories 90, 91 and 92 and determines a present location of the magnet rotor on the basis of the fetched peak values. According to a commutation scheme, controller 40 provides a corresponding driving control signal to switching-driving section 30 so that the rotor rotates in a desired direction by up to a desired angle in accordance with a commutation scheme for running the motor based on a determined rotor position.
As an example of the apparatus for controlling the rotation of the brushless motor, U.S. Pat. No. 5,382,890 discloses an integrated circuit driver for the brushless motor having an encoder which includes a plurality of Hall-effect sensors operative for providing commutation information to a motor controller. The driver includes a commutation decoding section for decoding the commutation information from the Hall-effect sensors and an analog current limiter.
In the above conventional apparatus for controlling the position of the motor, while the motor is rotating at a high velocity, controller 40 receives the information, which is necessary to control the rotational position, via sensors such as the Hall-effect sensors or extracts such information from a back electromotive force which is generated from phase coils 20, 21 and 22 during the rotation of the magnet rotor.
Meanwhile, the more slower motor 10 rotates, the smaller the value of the back electromotive force or an output from the sensor becomes, so that those sensed signals are difficult to use for detecting a correct rotor position. Namely, since a reliability of the control considerably decreases at a low velocity, only a control of a transient state, i.e., a coercive driving, for boosting the velocity of motor 10 to a high velocity is executed. The peak values which are selected by comparator 80 are stored into first, second and third memories 90, 91 and 92.
In a control system for the purpose of a low-speed control, an algorithm for determining a rotor position is utilized and thereby, the reliability to the low-speed control is in a high level, whereas in a high-speed mode, this system is not adapted to a control for high-speed rotation of the motor due to a time which is spent on determining a position of the rotor.
Further, in the above apparatus for controlling the position or the rotational velocity of sensorless and brushless DC motor 10, since the test current has to be amplified by amplifier 60 before the peak values of a small test current are detected by peak detector 50, and since the peak values have to be held for a time by sample & hold section 70 before the peak values of the test current detected by the first and second peak detectors are provided to comparator 80, a circuit configuration thereof becomes complicated. If amplifier 60 is not included in the apparatus, one of the peak values of the test current is not differentiated from the other peak values, so that a reliability of the operation of controller 40 for determining the rotor position considerably decreases.
Also, since those memories into which the peak values selected by comparator 80 are stored have relatively high prices, a unit cost of manufacturing the circuit for controlling the rotation of the motor increases.